FIGS. 6a and 6b are partial sectional views of a rough structure of a human eye. FIG. 6a is a view when a far point is seen, in which since a ciliary muscle (circular muscle) 102 is relaxed, a lens 100 is pulled by the tensile force of a choroid 104, its thickness becomes thin, and its curvature becomes small. On the other hand, FIG. 6b is a view when a near point is seen, in which the tensile force of the choroid 104 to extend the lens 100 is relieved by the contraction of the ciliary muscle (circular muscle) 102, the lens 100 swells by its own elasticity, the thickness becomes thick, and the curvature becomes large. By the mechanism as stated above, the curvature (focal distance) of the lens 100 is adjusted according to the distance from an object which is seen by the eye, and the object can be clearly sensed. Further, in order to more clearly sense the object, the iris (see FIG. 8) is used to adjust the diameter of the pupil, the angle composed by binocular visual lines is adjusted according to the distance from the object, and convergence (inward movement) and divergence (outward movement) is performed.
Incidentally, the far point is an external point, an image of which is formed on the fovea centralis of the retina when no adjustment of thickness of the lens 100 is made. Besides, the near point is an external point, an image of which is formed on the fovea centralis of the retina when the adjustment of thickness of the lens 100 is extremely made.
In recent years, children start to watch from an early age a television (TV), a TV game, a personal computer or the like for a long time resulting with increase of myopia children. Some causes of the myopia are generally known, and for example, it is regarded as one cause that when time for watching an object at the near point becomes long, the contraction state of the foregoing ciliary muscle 102 becomes long, the state in which the curvature of the lens 100 is large (the lens becomes thick) continues long, and the visual axis (distance from the lens 100 to the retina) becomes long.
Besides, although there are variations among individuals, from the age of approximately 40 years, the near point moves away, and presbyopia in which a near object can not be clearly sensed progresses. It is regarded that one of the main causes is the weakening of the ciliary muscle 102.
Incidentally, non-patent document, Modern Textbook of Ophthalmology (GENDAI NO GANKAGAKU) the seventh edition, Takashi Tokoro, Jun Kanai, Kanehara & Co., Ltd. also describes the cause of myopia and presbyopia.
Conventionally, an apparatus for restoring vision decreased due to the myopia or the like is proposed. For example, patent document JP-A-6-339501 discloses a vision restoration apparatus in which a gaze plate on which a mark is displayed is reciprocated, and a user gazes at the approaching and retreating mark, so that the training of the eyes is performed.
However, in the conventional vision restoration apparatus, since the size of the mark displayed on the gaze plate is constant, there has been a problem that especially when the mark approaches the user, it is hard to bring the mark into focus, and it becomes difficult to clearly see it. It is considered that this is because when the mark approaches the user, the size of the image of the mark formed on the retina of the eye of the user watching the mark becomes large, the amount of information sent to the brain increases, and it becomes difficult to control the ocular imaging adjustment functions of the ciliary muscle 102 and the like.
The invention has been made in view of the above conventional problems, and its object is to provide an eyesight improving device which improves ocular imaging adjustment functions and is easy to use.